Additive manufacturing of three-dimensional articles

ABSTRACT

Provided is a method for forming a three dimensional article comprising the steps of: providing at least one electron beam source emitting an electron beam for at least one of heating or fusing said powder material, where said electron beam source comprises a cathode, an anode, and a grid between said cathode and anode; controlling the electron beam source in at least two modes during said formation of said three dimensional article; applying a predetermined accelerator voltage between said cathode and said anode; applying a predetermined number of different grid voltages between said grid and said cathode for producing a corresponding predetermined number of electron beam currents; and at least one of creating or updating a look-up table or mathematical function during one of the at least two modes, wherein said look-up table or mathematical function defines a relationship between a desired electron beam current and an applied grid voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S.Nonprovisional patent application Ser. No. 15/450,358, filed on Mar. 6,2017, which is a divisional patent application of U.S. Nonprovisionalpatent application Ser. No. 14/547,530 now issued U.S. Pat. No.9,802,253, filed on Nov. 19, 2014, which further claims priority to andthe benefit of U.S. Provisional Patent Application Ser. No. 61/916,478,filed Dec. 16, 2013, and U.S. Provisional Patent Application Ser. No.61/917,769, filed Dec. 18, 2013, the contents of all of which as arehereby incorporated by reference in their entirety.

BACKGROUND Related Field

The present invention relates to a method for additive manufacturing ofa three dimensional article by successively fusing individual layers ofpowder material.

Description of Related Art

Freeform fabrication or additive manufacturing is a method for formingthree-dimensional articles through successive fusion of chosen parts ofpowder layers applied to a worktable.

An additive manufacturing apparatus may comprise a work table on whichthe three-dimensional article is to be formed, a powder dispenser orpowder distributor, arranged to lay down a thin layer of powder on thework table for the formation of a powder bed, a high energy beam fordelivering energy to the powder whereby fusion of the powder takesplace, elements for control of the energy given off by the energy beamover the powder bed for the formation of a cross section of thethree-dimensional article through fusion of parts of the powder bed, anda controlling computer, in which information is stored concerningconsecutive cross sections of the three-dimensional article. Athree-dimensional article is formed through consecutive fusions ofconsecutively formed cross sections of powder layers, successively laiddown by the powder dispenser.

In additive manufacturing a short manufacturing time and high quality ofthe finalized product is of outmost importance. Desired materialproperties of the final product may depend on the ability to control thefusion process. One important parameter is the ability to fast andaccurately control the actual beam output during the fusion process. Inmost electron beam sources the output current from the source may varyover time. If not having a full control of this variation in the beamcurrent over time, there is a great risk that the actual materialproperties of the final product will deviate from the desired materialproperties.

BRIEF SUMMARY

An object of the invention is to provide a method which fast andaccurately controls the beam current from an electron beam source in anadditive manufacturing process for improving the materialcharacteristics of the manufactured 3-dimensional article.

The above mentioned object is achieved by the features in the methodaccording to claim 1.

In a first aspect of the invention it is provided a method for forming athree-dimensional article through successively depositing individuallayers of powder material that are fused together so as to form thearticle, the method comprising the steps of: providing at least oneelectron beam source emitting an electron beam for heating and/or fusingthe powder material, where the electron beam source comprises a cathode,an anode, and a grid between the cathode and anode, controlling theelectron beam source in a first mode when the formation of the threedimensional article is in a first process step, controlling the electronbeam source in a second mode when the formation of the three dimensionalarticle is in a second process step, wherein an electron beam currentfrom the electron beam source is controlled in a feed-forward mode inthe first mode and the electron beam current is controlled in afeed-back mode in the second mode.

The advantage of the present invention is that the electron beam currentmay be controlled differently depending on process step. Some processsteps may require accurate electron beam current while other processsteps are more or less insensitive to the manipulation of the electronbeam current. This insight may be used in order to improve the endquality of the three-dimensional article.

In an example embodiment of the present invention the first process stepis the fusion of the powder material for forming the three-dimensionalarticle.

During the fusion of the three-dimensional article the accuracy of theelectron beam current may be critical for achieving particular materialcharacteristics. A desired electron beam current is achieved by feedingforward a predetermined steering parameter to the electron beam source.

The method according to any one of claim 1-2, wherein the second processstep is one of the group of: preheating of the surface prior to applyinga new powder layer onto the surface, preheating of a new powder layer,powder distribution or post heat treatment of an already fused powderlayer. During the preheating, post heat treatment or powder distributionthe accuracy of the value of the electron beam current is not criticalfor achieving the desired material characteristics. In the secondprocess step the steering parameter may be configured or updated forachieving a predetermined electron beam current. The steering parametermay be stored in a look up table or transformed into a mathematicalfunction. The look-up table or mathematical function may define arelationship between the steering parameter and the electron beamcurrent.

In another example embodiment the method further comprising the stepsof: applying a predetermined fixed accelerator voltage between thecathode and the anode, applying a predetermined number of different gridvoltages between the grid and the cathode for producing a correspondingpredetermined number of electron beam currents, creating or updating alook-up table or mathematical function during the second mode whereinthe look-up table or mathematical function defines a relationshipbetween a desired electron beam current and an applied grid voltage.

In the second process step when the electron beam current is not usedfor fusing the powder material, one may update or create therelationship between the steering parameter and the electron beamcurrent. The grid voltage may be set between two different extremevalues for creating maximum electron beam current and zero electron beamcurrent. A predetermined number of different grid voltages between thesetwo extreme values may be applied while measuring the actual electronbeam current. The resulting measurement data may be extrapolated inorder to achieve the necessary accuracy. The measurement data may bestored in a look-up table or transformed to a mathematical function,i.e., the actual electron beam current is feed-back where it later canbe retrieved from.

In still another example embodiment the method further comprising thesteps of: comparing a first actual electron beam current with a firstdesired electron beam current, updating the look-up table ormathematical function if the difference between the first actual andfirst desired electron beam currents is greater than a predeterminedvalue.

After having used a particular look-up table or mathematical function anumber of times, the look-up table or mathematical function may not beup to date, i.e., the applied grid voltage will not result in a desiredelectron beam current. The reason for the mismatch after a certainperiod of usage is that the cathode element becomes more and more used.For this reason it may be necessary to update the electron beam currentas a function of the grid voltage after a certain period of time. Thetrigger for this update may be when the measurement of an actual beamcurrent deviates more than a predetermined amount from a desiredelectron beam current.

In yet another example embodiment the updating is instead performedafter fusing a predetermined number of layers of the three-dimensionalarticle. It may be known beforehand that the electron beam current maybe out of specification for a given applied grid voltage after a numberof fused powder layers and therefore the update of the electron beamcurrent as a function of the grid voltage is performed in a periodicallywhich is determined before the actual formation of the three-dimensionalarticle starts.

In still another example embodiment the updating is instead performedbetween the fusion process of each layer. In order to always use themost accurate electron beam current available the update of the electronbeam current as a function of the grid voltage may be performed betweeneach fusion process of each layer. This may become useful when the buildarea is increasing in size.

In still another example embodiment the method further comprising thesteps of: retrieving the predetermined grid voltage for producing thedesired electron beam current from the look-up table or a mathematicalfunction, changing the predetermined grid voltage from a first gridvoltage to a second grid voltage during the first mode for changing theelectron beam current from a first value to a second desired valueduring fusion of a predetermined layer.

Different electron beam currents may be used when fusing a particularpowder layer. Switching from a first electron beam current to a secondelectron beam current may be performed by amending the grid voltage froma first grid voltage to a second grid voltage. The grid voltages areretrieved from a look-up table or from a mathematical function. It maybe known beforehand when the electron beam current has to be changedfrom a first level to a second level. The optimal electron beam currentmay be known from simulations of the manufacturing of the specific threedimensional article for achieving predetermined materialcharacteristics.

In still another example embodiment the predetermined grid voltage ischanged from a first grid voltage to a second grid voltage during fusionof at least one individual scan line for changing the electron beamcurrent in the scan line from a first value to a second desired value.

The change of electron beam current from a first value to a second valueis performed by amending the grid voltage from a first to a secondvalue. Since this may be done relatively quickly the electron beamcurrent may be changed during a specific scan line. This may beadvantageous for decreasing the manufacturing time while at the sametime achieving the desired material characteristics.

In another aspect of the present invention it is provided a programelement configured and arranged when executed on a computer a method forforming a three-dimensional article through successively depositingindividual layers of powder material that are fused together so as toform the article, the method comprising the steps of: providing at leastone electron beam source emitting an electron beam for heating and/orfusing the powder material, where the electron beam source comprising acathode, an anode, and a grid between the cathode and anode, controllingthe electron beam source in a first mode when the formation of the threedimensional article is in a first process step, controlling the electronbeam source in a second mode when the formation of the three dimensionalarticle is in a second process step, wherein an electron beam currentfrom the electron beam source is controlled in a feed-forward mode inthe first mode and the electron beam current is controlled in afeed-back mode in the second mode.

In still another aspect of the present invention it is provided acomputer readable medium having stored thereon the program element.

In yet another aspect of the present invention it is provided anon-transitory computer program product comprising at least onenon-transitory computer-readable storage medium having computer-readableprogram code portions embodied therein. In these embodiments, thecomputer-readable program code portions comprises: an executable portionconfigured for controlling an electron beam source in a first mode whenformation of a three dimensional article is in a first process step, theelectron beam source emitting an electron beam for at least one ofheating or fusing individual layers of a powder material together so asto form the three-dimensional article, the electron beam sourcecomprising a cathode, an anode, and a grid between the cathode andanode; and an executable portion configured for controlling the electronbeam source in a second mode when the formation of the three dimensionalarticle is in a second process step, wherein an electron beam currentfrom the electron beam source is controlled in a feed-forward mode inthe first mode and the electron beam current is controlled in afeed-back mode in the second mode.

In yet another aspect of the present invention it is provided a methodfor forming a three-dimensional article through successively depositingindividual layers of powder material that are fused together so as toform the article. The method comprises the steps of: providing at leastone electron beam source emitting an electron beam for at least one ofheating or fusing the powder material, where the electron beam sourcecomprises a cathode, an anode, and a grid between the cathode and anode;controlling the electron beam source in at least two modes during theformation of the three dimensional article; applying a predeterminedaccelerator voltage between the cathode and the anode; applying apredetermined number of different grid voltages between the grid and thecathode for producing a corresponding predetermined number of electronbeam currents; and at least one of creating or updating a look-up tableor mathematical function during one of the at least two modes, whereinthe look-up table or mathematical function defines a relationshipbetween a desired electron beam current and an applied grid voltage.

All examples and exemplary embodiments described herein are non-limitingin nature and thus should not be construed as limiting the scope of theinvention described herein. Still further, the advantages describedherein, even where identified with respect to a particular exemplaryembodiment, should not be necessarily construed in such a limitingfashion.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 depicts, in a schematic view, an example embodiment of anelectron beam source in which the inventive method may be implemented;

FIG. 2 depicts, in a schematic view, an example embodiment of anapparatus for producing a three dimensional product which may have anelectron beam source according to FIG. 1;

FIG. 3 depicts the grid potential-cathode potential as a function ofelectron beam current for different emissivity of a filament in anelectron beam source;

FIG. 4 is a block diagram of an exemplary system 1020 according tovarious embodiments;

FIG. 5A is a schematic block diagram of a server 1200 according tovarious embodiments; and

FIG. 5B is a schematic block diagram of an exemplary mobile device 1300according to various embodiments.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

Various embodiments of the present invention will now be described morefully hereinafter with reference to the accompanying drawings, in whichsome, but not all embodiments of the invention are shown. Indeed,embodiments of the invention may be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure willsatisfy applicable legal requirements. Unless otherwise defined, alltechnical and scientific terms used herein have the same meaning ascommonly known and understood by one of ordinary skill in the art towhich the invention relates. The term “or” is used herein in both thealternative and conjunctive sense, unless otherwise indicated. Likenumbers refer to like elements throughout.

Still further, to facilitate the understanding of this invention, anumber of terms are defined below. Terms defined herein have meanings ascommonly understood by a person of ordinary skill in the areas relevantto the present invention. Terms such as “a”, “an” and “the” are notintended to refer to only a singular entity, but include the generalclass of which a specific example may be used for illustration. Theterminology herein is used to describe specific embodiments of theinvention, but their usage does not delimit the invention, except asoutlined in the claims.

The term “three-dimensional structures” and the like as used hereinrefer generally to intended or actually fabricated three-dimensionalconfigurations (e.g., of structural material or materials) that areintended to be used for a particular purpose. Such structures, etc. may,for example, be designed with the aid of a three-dimensional CAD system.

The term “electron beam” as used herein in various embodiments refers toany charged particle beam. The sources of charged particle beam caninclude an electron gun, a linear accelerator and so on.

FIG. 2 depicts an embodiment of a freeform fabrication or additivemanufacturing apparatus 21 in which the inventive method according tothe present invention may be implemented.

The apparatus 21 comprising an electron beam gun 6; deflection coils 7;two powder hoppers 4, 14; a build platform 2; a build tank 10; a powderdistributor 28; a powder bed 5; and a vacuum chamber 20.

The vacuum chamber 20 is capable of maintaining a vacuum environment viaa vacuum system, which system may comprise a turbo molecular pump, ascroll pump, an ion pump and one or more valves which are well known toa skilled person in the art and therefore need no further explanation inthis context. The vacuum system is controlled by a control unit 8.

The electron beam gun 6 is generating an electron beam which is used forpre heating of the powder, melting or fusing together powder materialprovided on the build platform 2 or post heat treatment of the alreadyfused powder material. At least a portion of the electron beam gun 6 maybe provided in the vacuum chamber 20. The control unit 8 may be used forcontrolling and managing the electron beam emitted from the electronbeam gun 6. At least one focusing coil (not shown), at least onedeflection coil 7, an optional coil for astigmatic correction (notshown) and an electron beam power supply (not shown) may be electricallyconnected to the control unit 8. In an example embodiment of theinvention the electron beam gun 6 may generate a focusable electron beamwith an accelerating voltage of about 15-60 kV and with a beam power inthe range of 3-10 kW. The pressure in the vacuum chamber may be 10⁻³mbar or lower when building the three-dimensional article by fusing thepowder layer by layer with the energy beam.

The powder hoppers 4, 14 comprise the powder material to be provided onthe build platform 2 in the build tank 10. The powder material may forinstance be pure metals or metal alloys such as titanium, titaniumalloys, aluminum, aluminum alloys, stainless steel, Co—Cr alloys, nickelbased super alloys, etc.

The powder distributor 28 is arranged to lay down a thin layer of thepowder material on the build platform 2. During a work cycle the buildplatform 2 will be lowered successively in relation to a fixed point inthe vacuum chamber. In order to make this movement possible, the buildplatform 2 is in one embodiment of the invention arranged movably invertical direction, i.e., in the direction indicated by arrow P. Thismeans that the build platform 2 starts in an initial position, in whicha first powder material layer of necessary thickness has been laid down.Means for lowering the build platform 2 may for instance be through aservo engine equipped with a gear, adjusting screws, etc. The servoengine may be connected to the control unit 8.

An electron beam may be directed over the build platform 2 causing thefirst powder layer to fuse in selected locations to form a first crosssection of the three-dimensional article 3. The beam is directed overthe build platform 2 from instructions given by the control unit 8. Inthe control unit 8 instructions for how to control the electron beam foreach layer of the three-dimensional article is stored. The first layerof the three dimensional article 3 may be built on the build platform 2,which may be removable, in the powder bed 5 or on an optional startplate 16. The start plate 16 may be arranged directly on the buildplatform 2 or on top of a powder bed 5 which is provided on the buildplatform 2.

After a first layer is finished, i.e., the fusion of powder material formaking a first layer of the three-dimensional article, a second powderlayer is provided on the build platform 2. The thickness of the secondlayer may be determined by the distance the build platform is lowered inrelation to the position where the first layer was built. The secondpowder layer is in various embodiments distributed according to the samemanner as the previous layer. However, there might be alternativemethods in the same additive manufacturing machine for distributingpowder onto the work table. For instance, a first layer may be providedvia a first powder distributor 28, a second layer may be provided byanother powder distributor. The design of the powder distributor isautomatically changed according to instructions from the control unit 8.A powder distributor 28 in the form of a single rake system, i.e., whereone rake is catching powder fallen down from both a left powder hopper 4and a right powder hopper 14, the rake as such can change design.

After having distributed the second powder layer on the build platform,the energy beam is directed over the work table causing the secondpowder layer to fuse in selected locations to form a second crosssection of the three-dimensional article. Fused portions in the secondlayer may be bonded to fused portions of the first layer. The fusedportions in the first and second layer may be melted together by meltingnot only the powder in the uppermost layer but also remelting at least afraction of a thickness of a layer directly below the uppermost layer.

Sometimes it may be necessary to consider the charge distribution thatis created in the powder as the electrons hit the powder bed 5. Thecharge distribution density depends on the following parameters: beamcurrent, electron velocity (which is given by the accelerating voltage),beam scanning velocity, powder material and electrical conductivity ofthe powder, i.e., mainly the electrical conductivity between the powdergrains. The latter is in turn a function of several parameters, such asthe non-limiting examples of temperature, degree of sintering and powdergrain size/size distribution.

Thus, for a given powder, i.e., a powder of a certain material with acertain grain size distribution, and a given accelerating voltage, it ispossible, by varying the beam current (and thus the beam power) and thebeam scanning velocity, to affect the charge distribution.

By varying these parameters in a controlled way, the electricalconductivity of the powder can gradually be increased by increasing thetemperature of the powder. A powder that has a high temperature obtainsa considerably higher conductivity which results in a lower density ofthe charge distribution since the charges quickly can diffuse over alarge region. This effect is enhanced if the powder is allowed to beslightly sintered during a pre-heating process. When the conductivityhas become sufficiently high, the powder can be fused together, i.e.,melted or fully sintered, with predetermined values of the beam currentand beam scanning velocity.

FIG. 1 depicts, in a schematic view, an exemplary embodiment of anelectron beam source in which the inventive method may be implemented.The electron beam source 100 comprises a cathode 102, a grid 104 and ananode 106. Electrons emitted at the cathode 102 being on negativepotential are accelerated towards the anode 106 and finally a targetsurface 118. A grid 104 is set at a predetermined distance from thecathode 102. The cathode 102 may be provided with a voltage which maycause the cathode to heat up, where upon the cathode 102 releaseselectrons by thermionic emission.

An accelerator voltage 160 is provided between the cathode and the anode106. The accelerator voltage 160 causes the emitted electrons from thecathode 102 to accelerate towards the anode 106 thus establishing anelectron beam 120. The electron beam 120 may impinge on a substratesurface 118, which may be a powder layer in an additive manufacturingprocess. In order to guide and focus the electron beam there may furtherbe arranged at least one focusing coil and at least one deflection coil.

In the electron beam source 100 the grid 104 is provided between thecathode 102 and the anode 106. The grid 104 may be arranged as a platehaving an aperture. The aperture may be aligned with the cathode 102.The size of the aperture in the grid 104 may correspond to a crosssection of the electron beam 120 at the position of the grid 104.

A grid voltage 180 may be provided between the grid 104 and the cathode102 and may be adjusted between a negative blocking voltage and a fullpower voltage and thereby adjusting an electron beam current between0-maximum electron beam current. In FIG. 1 the cathode 102 may beprovided with a negative potential of −20 kV to −100 kV. A firstconnection point 110 of the accelerator voltage 160 and a firstconnection point 114 of the grid voltage 180 may be fixed to the samepotential of −20 kV to −100 kV. A second connection point 108 of theaccelerator voltage 160 may be provided with ground potential voltage. Asecond connection point 112 of the grid voltage 180 may be variedbetween the negative blocking voltage and the full power voltage. Asecond control unit 150 may be controlling the voltage on the secondconnection point 112 of the grid voltage in order to adjust the electronbeam current to a desired value. The second control unit 150 may be aphysically separate control unit in connection with the control unit 8or fully integrated in the control unit 8.

The target surface 118 may be set to ground potential or a positivepotential. The electron beam source 100 may also comprise means 170 fordetecting the actual electron beam current. An example means fordetecting the electron beam current on the target surface may be todetect the actual loading of the high voltage source providing theaccelerator voltage 160, indicated by box 170 in FIG. 1. This may bedone by simply measuring the electron beam passing between the first andsecond connection points 110 and 108 respectively. If the cathode isprovided with a fixed negative voltage of −60 kV the negative blockingvoltage may be around −61 kV, i.e., the second connection point 112 ofthe grid voltage is set at −61 kV and the first connection point 114 isset to −60 kV, for blocking the electrons by the grid 104. If startingto decrease the negative blocking voltage at the second connection point112, some of the electrons emitted from the cathode will be allowed topass the grid 104. By varying the grid voltage in this exampleembodiment between −61 kV to ˜−60 kV, when the cathode is provided witha fixed negative potential of −60 kV, the electron beam current may varyfrom 0 mA-maximum electron beam current which may be 25 mA for apredetermined size and shape of the cathode and a predetermined size andshape of the aperture in the grid 104. Other accelerator voltages and/orother size, shape and emissivity of the cathode and/or other size andshape of the aperture in the grid may affect the maximum electron beamcurrent to be higher or lower than the exemplified 25 mA.

FIG. 3 depicts the grid potential-cathode potential as a function ofelectron beam current for different emissivity of a filament. When thegrid voltage 180 is at a sufficiently high negative potential, i.e., thepotential on connection point 112 is provided with a sufficient negativepotential (negative blocking potential) compared to the negativepotential on connection point 114, the electrons emanating from thecathode 102 will be blocked (repelled) by the negative potential on thegrid 104 resulting in no electrons passing through the aperture in thegrid 104. In such a case we are at the leftmost position in the graph inFIG. 3, i.e., zero electron beam current. As the potential differencebetween the cathode 102 and grid 104 is decreasing the electron beamcurrent is increasing, i.e., we are moving to the right in the graph inFIG. 3. U_(C) represents the cathode potential and U_(G) represents thegrid potential.

A cathode 102 at different temperatures may emanate different amounts ofelectrons. In FIG. 3 it is illustrated 4 different graphs 310, 320, 330and 340. A first graph 310 may represent a cathode at a firsttemperature. A second graph 320 may represent a cathode at a secondtemperature. A third graph 330 may represent a cathode at a thirdtemperature. A fourth graph 310 may represent a cathode at a fourthtemperature. The first temperature<the second temperature<the thirdtemperature<the fourth temperature. Not only the temperature of thecathode may affect the numbers of emanating electrons. When the cathodeis used its emissivity of electron may change in a similar manner asdepicted in FIG. 3. An unused cathode may be represented by graph 340.The more the cathode 102 is used the last portion of the graph isshifted to the left. A combination of a change in temperature of thecathode and the degree of use may also be represented by the differentgraphs in FIG. 3, i.e., for relatively cold cathodes and well used thelast portion will be shifted to the left and for a relatively hot andnew cathode the graph will be shifted to the right.

The graph in FIG. 3 may be defined by applying a predetermined number ofdifferent U_(G)-U_(C) potentials and measuring the resulting electronbeam current for the U_(G)-U_(C) potentials. The graph may beapproximated by a mathematical expression, for instance a polynomialwhich is fitted to the graph.

In an example embodiment of the present invention it is provided amethod for forming a three-dimensional article through successivelydepositing individual layers of powder material that are fused togetherso as to form the article. At least one electron beam source is providedfor emitting an electron beam for heating and/or fusing the powdermaterial, where the electron beam source comprises a cathode, an anode,and a grid between the cathode and anode. The electron beam source iscontrolled in a first mode when the formation of the three dimensionalarticle is in a first process step. The electron beam is controlled in asecond mode when the formation of the three dimensional article is in asecond process step. In the first mode an electron beam current from theelectron beam source is controlled in a feed-forward mode and in thesecond mode the electron beam current is controlled in a feed-back mode.

In the feed-back mode the grid potential as a function of electron beamcurrent is created or updated. This may be done by measuring the actualelectron beam currents for different applied grid voltages. Theresulting measurement may be stored in a look-up table and/or beapproximated by a mathematical function. The feed-back mode may beaccomplished during preheating of a non-fused powder layer, post heattreatment of a fused powder layer, powder distribution or machineidling, i.e., the feed-back mode may be performed during themanufacturing process steps where the accuracy of the electron beamcurrent is not critical. The mathematical function may for instance beof the type A+Bx+Cx²+Dx³ or any other suitable mathematical functionwhich will best fit the actual measurement data. If using a look-uptable the data points in between actual measured data point may besuitably extrapolated in order to achieve a desired accuracy of theelectron beam current. An update of the U_(C)-U_(G) as a function of theelectron beam current may be performed once in between each fusion ofthe individual powder layers. The creation of the look-up table ormathematical function may be performed before starting a new manufactureof a three-dimensional article. This will make sure that the correctelectron beam fusion current is used when fusing the powder layer fromthe first powder layer.

In the feed forward mode a predetermined grid potential is applied forachieving a predetermined electron beam current. The grid potential istaken from a look-up table or calculated from a mathematical function.The feed forward mode is used during the fusion process of the threedimensional article, i.e., when powder material is melted or fused bythe electron beam impinged on the powder layer. By extracting thecorrect grid voltage for achieving a desired electron beam current fromeither a look up table or a mathematical function the electron beamcurrent may be switched from a first predetermined electron beam currentto a second predetermined electron beam current by just switching thepotential on the grid from a first grid potential to a second gridpotential. This may enable fast switching of the electron beam currentduring the fusion process with accuracy from a first electron beamcurrent to a second electron beam current. This may be helpful when anelectron beam current has to be switched from a first electron beamcurrent to a second electron beam current during a scan line of theelectron beam in order to achieve final material characteristics. Asimulation before starting the actual build of the three dimensionalarticle may show that the electron beam has to be changed during aparticular scan line for a particular reason, which may be materialcharacteristics, final dimension accuracy, or maintenance of the buildtemperature. By using the inventive feed forward mode for controllingthe electron beam current during the fusion process the accuracy andpredictability of the material characteristics of the three dimensionalarticle may be improved. By changing the grid potential from a firstvalue to a second value, the electron beam current may instantaneouslychange from a first electron beam current to a second desired electronbeam current. The fast response of the amendment of the grid potentialand the corresponding electron beam current makes it suitable as anaddressing method for electron beam current in an additive manufacturingprocess where the electron beam may need to be amended several timesduring a small time interval. A sufficiently quick change in theelectron beam current may for some applications be the key factor for asuccessful 3-dimensional article with the desired material propertiesand dimensional tolerances.

In the feed-forward mode a predetermined grid potential is applied forachieving a predetermined electron beam current on the powder surfacefor fusing the powder. Here one is using the grid potential as afunction of beam current which is already created and updated. This willmake sure that a desired electron beam current will impinge on thepowder layer for a predetermined grid potential. This may also enable afast switching during a fusion process from a first electron beamcurrent to a second electron beam current. This may be necessary duringa scan line depending on which, when and/or where a specific type ofstructure to be melted.

In an example embodiment of the present invention it is provided amethod for forming a three-dimensional article through successivelydepositing individual layers of powder material that are fused togetherso as to form the article, the method comprising the steps of: providingat least one electron beam source emitting an electron beam for heatingand/or fusing the powder material, where the electron beam sourcecomprising a cathode, an anode, and a grid between the cathode andanode, and changing the electron beam current from the electron beamsource from a first electron beam current to a second electron beamcurrent by switching an applied potential on the grid from a first valueto a second value.

The switching may be performed during the fusion of a particular layerof the three dimensional article. In another example embodiment theswitching may be performed during the fusion of a particular scan line.The grid potential and the corresponding electron beam currents may bestored in a look up table or be represented by a mathematical function.The look-up table or the mathematical function may be created or updatedduring preheating of the surface prior to applying a new powder layeronto the surface, preheating of a new powder layer, powder distributionor post heat treatment of an already fused powder layer.

In another aspect of the invention it is provided a program elementconfigured and arranged when executed on a computer to implement amethod for forming a three-dimensional article through successivelydepositing individual layers of powder material that are fused togetherso as to form the article, the method comprising the steps of: providingat least one electron beam source emitting an electron beam for heatingand/or fusing the powder material, where the electron beam sourcecomprising a cathode, an anode, and a grid between the cathode andanode, controlling the electron beam source in a first mode when theformation of the three dimensional article is in a first process step,controlling the electron beam source in a second mode when the formationof the three dimensional article is in a second process step, wherein anelectron beam current from the electron beam source is controlled in afeed-forward mode in the first mode and the electron beam current iscontrolled in a feed-back mode in the second mode. The program may beinstalled in a computer readable storage medium. The computer readablestorage medium may be the control unit 8, the control unit 150, oranother separate and distinct control unit. The computer readablestorage medium and the program element, which may comprisecomputer-readable program code portions embodied therein, may further becontained within a non-transitory computer program product. Furtherdetails regarding these features and configurations are provided, inturn, below.

As mentioned, various embodiments of the present invention may beimplemented in various ways, including as non-transitory computerprogram products. A computer program product may include anon-transitory computer-readable storage medium storing applications,programs, program modules, scripts, source code, program code, objectcode, byte code, compiled code, interpreted code, machine code,executable instructions, and/or the like (also referred to herein asexecutable instructions, instructions for execution, program code,and/or similar terms used herein interchangeably). Such non-transitorycomputer-readable storage media include all computer-readable media(including volatile and non-volatile media).

In one embodiment, a non-volatile computer-readable storage medium mayinclude a floppy disk, flexible disk, hard disk, solid-state storage(SSS) (e.g., a solid state drive (SSD), solid state card (SSC), solidstate module (SSM)), enterprise flash drive, magnetic tape, or any othernon-transitory magnetic medium, and/or the like. A non-volatilecomputer-readable storage medium may also include a punch card, papertape, optical mark sheet (or any other physical medium with patterns ofholes or other optically recognizable indicia), compact disc read onlymemory (CD-ROM), compact disc compact disc-rewritable (CD-RW), digitalversatile disc (DVD), Blu-ray disc (BD), any other non-transitoryoptical medium, and/or the like. Such a non-volatile computer-readablestorage medium may also include read-only memory (ROM), programmableread-only memory (PROM), erasable programmable read-only memory (EPROM),electrically erasable programmable read-only memory (EEPROM), flashmemory (e.g., Serial, NAND, NOR, and/or the like), multimedia memorycards (MMC), secure digital (SD) memory cards, SmartMedia cards,CompactFlash (CF) cards, Memory Sticks, and/or the like. Further, anon-volatile computer-readable storage medium may also includeconductive-bridging random access memory (CBRAM), phase-change randomaccess memory (PRAM), ferroelectric random-access memory (FeRAM),non-volatile random-access memory (NVRAM), magnetoresistiverandom-access memory (MRAM), resistive random-access memory (RRAM),Silicon-Oxide-Nitride-Oxide-Silicon memory (SONOS), floating junctiongate random access memory (FJG RAM), Millipede memory, racetrack memory,and/or the like.

In one embodiment, a volatile computer-readable storage medium mayinclude random access memory (RAM), dynamic random access memory (DRAM),static random access memory (SRAM), fast page mode dynamic random accessmemory (FPM DRAM), extended data-out dynamic random access memory (EDODRAM), synchronous dynamic random access memory (SDRAM), double datarate synchronous dynamic random access memory (DDR SDRAM), double datarate type two synchronous dynamic random access memory (DDR2 SDRAM),double data rate type three synchronous dynamic random access memory(DDR3 SDRAM), Rambus dynamic random access memory (RDRAM), TwinTransistor RAM (TTRAM), Thyristor RAM (T-RAM), Zero-capacitor (Z-RAM),Rambus in-line memory module (RIMM), dual in-line memory module (DIMM),single in-line memory module (SIMM), video random access memory VRAM,cache memory (including various levels), flash memory, register memory,and/or the like. It will be appreciated that where embodiments aredescribed to use a computer-readable storage medium, other types ofcomputer-readable storage media may be substituted for or used inaddition to the computer-readable storage media described above.

As should be appreciated, various embodiments of the present inventionmay also be implemented as methods, apparatus, systems, computingdevices, computing entities, and/or the like, as have been describedelsewhere herein. As such, embodiments of the present invention may takethe form of an apparatus, system, computing device, computing entity,and/or the like executing instructions stored on a computer-readablestorage medium to perform certain steps or operations. However,embodiments of the present invention may also take the form of anentirely hardware embodiment performing certain steps or operations.

Various embodiments are described below with reference to block diagramsand flowchart illustrations of apparatuses, methods, systems, andcomputer program products. It should be understood that each block ofany of the block diagrams and flowchart illustrations, respectively, maybe implemented in part by computer program instructions, e.g., aslogical steps or operations executing on a processor in a computingsystem. These computer program instructions may be loaded onto acomputer, such as a special purpose computer or other programmable dataprocessing apparatus to produce a specifically-configured machine, suchthat the instructions which execute on the computer or otherprogrammable data processing apparatus implement the functions specifiedin the flowchart block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including computer-readableinstructions for implementing the functionality specified in theflowchart block or blocks. The computer program instructions may also beloaded onto a computer or other programmable data processing apparatusto cause a series of operational steps to be performed on the computeror other programmable apparatus to produce a computer-implementedprocess such that the instructions that execute on the computer or otherprogrammable apparatus provide operations for implementing the functionsspecified in the flowchart block or blocks.

Accordingly, blocks of the block diagrams and flowchart illustrationssupport various combinations for performing the specified functions,combinations of operations for performing the specified functions andprogram instructions for performing the specified functions. It shouldalso be understood that each block of the block diagrams and flowchartillustrations, and combinations of blocks in the block diagrams andflowchart illustrations, could be implemented by special purposehardware-based computer systems that perform the specified functions oroperations, or combinations of special purpose hardware and computerinstructions.

FIG. 4 is a block diagram of an exemplary system 1020 that can be usedin conjunction with various embodiments of the present invention. In atleast the illustrated embodiment, the system 1020 may include one ormore central computing devices 1110, one or more distributed computingdevices 1120, and one or more distributed handheld or mobile devices1300, all configured in communication with a central server 1200 (orcontrol unit) via one or more networks 1130. While FIG. 4 illustratesthe various system entities as separate, standalone entities, thevarious embodiments are not limited to this particular architecture.

According to various embodiments of the present invention, the one ormore networks 1130 may be capable of supporting communication inaccordance with any one or more of a number of second-generation (2G),2.5G, third-generation (3G), and/or fourth-generation (4G) mobilecommunication protocols, or the like. More particularly, the one or morenetworks 1130 may be capable of supporting communication in accordancewith 2G wireless communication protocols IS-136 (TDMA), GSM, and IS-95(CDMA). Also, for example, the one or more networks 1130 may be capableof supporting communication in accordance with 2.5G wirelesscommunication protocols GPRS, Enhanced Data GSM Environment (EDGE), orthe like. In addition, for example, the one or more networks 1130 may becapable of supporting communication in accordance with 3G wirelesscommunication protocols such as Universal Mobile Telephone System (UMTS)network employing Wideband Code Division Multiple Access (WCDMA) radioaccess technology. Some narrow-band AMPS (NAMPS), as well as TACS,network(s) may also benefit from embodiments of the present invention,as should dual or higher mode mobile stations (e.g., digital/analog orTDMA/CDMA/analog phones). As yet another example, each of the componentsof the system 5 may be configured to communicate with one another inaccordance with techniques such as, for example, radio frequency (RF),Bluetooth™, infrared (IrDA), or any of a number of different wired orwireless networking techniques, including a wired or wireless PersonalArea Network (“PAN”), Local Area Network (“LAN”), Metropolitan AreaNetwork (“MAN”), Wide Area Network (“WAN”), or the like.

Although the device(s) 1110-1300 are illustrated in FIG. 4 ascommunicating with one another over the same network 1130, these devicesmay likewise communicate over multiple, separate networks.

According to one embodiment, in addition to receiving data from theserver 1200, the distributed devices 1110, 1120, and/or 1300 may befurther configured to collect and transmit data on their own. In variousembodiments, the devices 1110, 1120, and/or 1300 may be capable ofreceiving data via one or more input units or devices, such as a keypad,touchpad, barcode scanner, radio frequency identification (RFID) reader,interface card (e.g., modem, etc.) or receiver. The devices 1110, 1120,and/or 1300 may further be capable of storing data to one or morevolatile or non-volatile memory modules, and outputting the data via oneor more output units or devices, for example, by displaying data to theuser operating the device, or by transmitting data, for example over theone or more networks 1130.

In various embodiments, the server 1200 includes various systems forperforming one or more functions in accordance with various embodimentsof the present invention, including those more particularly shown anddescribed herein. It should be understood, however, that the server 1200might include a variety of alternative devices for performing one ormore like functions, without departing from the spirit and scope of thepresent invention. For example, at least a portion of the server 1200,in certain embodiments, may be located on the distributed device(s)1110, 1120, and/or the handheld or mobile device(s) 1300, as may bedesirable for particular applications. As will be described in furtherdetail below, in at least one embodiment, the handheld or mobiledevice(s) 1300 may contain one or more mobile applications 1330 whichmay be configured so as to provide a user interface for communicationwith the server 1200, all as will be likewise described in furtherdetail below.

FIG. 5A is a schematic diagram of the server 1200 according to variousembodiments. The server 1200 includes a processor 1230 that communicateswith other elements within the server via a system interface or bus1235. Also included in the server 1200 is a display/input device 1250for receiving and displaying data. This display/input device 1250 maybe, for example, a keyboard or pointing device that is used incombination with a monitor. The server 1200 further includes memory1220, which preferably includes both read only memory (ROM) 1226 andrandom access memory (RAM) 1222. The server's ROM 1226 is used to storea basic input/output system 1224 (BIOS), containing the basic routinesthat help to transfer information between elements within the server1200. Various ROM and RAM configurations have been previously describedherein.

In addition, the server 1200 includes at least one storage device orprogram storage 210, such as a hard disk drive, a floppy disk drive, aCD Rom drive, or optical disk drive, for storing information on variouscomputer-readable media, such as a hard disk, a removable magnetic disk,or a CD-ROM disk. As will be appreciated by one of ordinary skill in theart, each of these storage devices 1210 are connected to the system bus1235 by an appropriate interface. The storage devices 1210 and theirassociated computer-readable media provide nonvolatile storage for apersonal computer. As will be appreciated by one of ordinary skill inthe art, the computer-readable media described above could be replacedby any other type of computer-readable media known in the art. Suchmedia include, for example, magnetic cassettes, flash memory cards,digital video disks, and Bernoulli cartridges.

Although not shown, according to an embodiment, the storage device 1210and/or memory of the server 1200 may further provide the functions of adata storage device, which may store historical and/or current deliverydata and delivery conditions that may be accessed by the server 1200. Inthis regard, the storage device 1210 may comprise one or more databases.The term “database” refers to a structured collection of records or datathat is stored in a computer system, such as via a relational database,hierarchical database, or network database and as such, should not beconstrued in a limiting fashion.

A number of program modules (e.g., exemplary modules 1400-1700)comprising, for example, one or more computer-readable program codeportions executable by the processor 1230, may be stored by the variousstorage devices 1210 and within RAM 1222. Such program modules may alsoinclude an operating system 1280. In these and other embodiments, thevarious modules 1400, 1500, 1600, 1700 control certain aspects of theoperation of the server 1200 with the assistance of the processor 1230and operating system 1280. In still other embodiments, it should beunderstood that one or more additional and/or alternative modules mayalso be provided, without departing from the scope and nature of thepresent invention.

In various embodiments, the program modules 1400, 1500, 1600, 1700 areexecuted by the server 1200 and are configured to generate one or moregraphical user interfaces, reports, instructions, and/ornotifications/alerts, all accessible and/or transmittable to varioususers of the system 1020. In certain embodiments, the user interfaces,reports, instructions, and/or notifications/alerts may be accessible viaone or more networks 1130, which may include the Internet or otherfeasible communications network, as previously discussed.

In various embodiments, it should also be understood that one or more ofthe modules 1400, 1500, 1600, 1700 may be alternatively and/oradditionally (e.g., in duplicate) stored locally on one or more of thedevices 1110, 1120, and/or 1300 and may be executed by one or moreprocessors of the same. According to various embodiments, the modules1400, 1500, 1600, 1700 may send data to, receive data from, and utilizedata contained in one or more databases, which may be comprised of oneor more separate, linked and/or networked databases.

Also located within the server 1200 is a network interface 1260 forinterfacing and communicating with other elements of the one or morenetworks 1130. It will be appreciated by one of ordinary skill in theart that one or more of the server 1200 components may be locatedgeographically remotely from other server components. Furthermore, oneor more of the server 1200 components may be combined, and/or additionalcomponents performing functions described herein may also be included inthe server.

While the foregoing describes a single processor 1230, as one ofordinary skill in the art will recognize, the server 1200 may comprisemultiple processors operating in conjunction with one another to performthe functionality described herein. In addition to the memory 1220, theprocessor 1230 can also be connected to at least one interface or othermeans for displaying, transmitting and/or receiving data, content or thelike. In this regard, the interface(s) can include at least onecommunication interface or other means for transmitting and/or receivingdata, content or the like, as well as at least one user interface thatcan include a display and/or a user input interface—as will be describedin further detail below. The user input interface, in turn, can compriseany of a number of devices allowing the entity to receive data from auser, such as a keypad, a touch display, a joystick or other inputdevice.

Still further, while reference is made to the “server” 1200, as one ofordinary skill in the art will recognize, embodiments of the presentinvention are not limited to traditionally defined server architectures.Still further, the system of embodiments of the present invention is notlimited to a single server, or similar network entity or mainframecomputer system. Other similar architectures including one or morenetwork entities operating in conjunction with one another to providethe functionality described herein may likewise be used withoutdeparting from the spirit and scope of embodiments of the presentinvention. For example, a mesh network of two or more personal computers(PCs), similar electronic devices, or handheld portable devices,collaborating with one another to provide the functionality describedherein in association with the server 1200 may likewise be used withoutdeparting from the spirit and scope of embodiments of the presentinvention.

According to various embodiments, many individual steps of a process mayor may not be carried out utilizing the computer systems and/or serversdescribed herein, and the degree of computer implementation may vary, asmay be desirable and/or beneficial for one or more particularapplications.

FIG. 5B provides an illustrative schematic representative of a mobiledevice 1300 that can be used in conjunction with various embodiments ofthe present invention. Mobile devices 1300 can be operated by variousparties. As shown in FIG. 5B, a mobile device 1300 may include anantenna 1312, a transmitter 1304 (e.g., radio), a receiver 1306 (e.g.,radio), and a processing element 1308 that provides signals to andreceives signals from the transmitter 1304 and receiver 1306,respectively.

The signals provided to and received from the transmitter 1304 and thereceiver 1306, respectively, may include signaling data in accordancewith an air interface standard of applicable wireless systems tocommunicate with various entities, such as the server 1200, thedistributed devices 1110, 1120, and/or the like. In this regard, themobile device 1300 may be capable of operating with one or more airinterface standards, communication protocols, modulation types, andaccess types. More particularly, the mobile device 1300 may operate inaccordance with any of a number of wireless communication standards andprotocols. In a particular embodiment, the mobile device 1300 mayoperate in accordance with multiple wireless communication standards andprotocols, such as GPRS, UMTS, CDMA2000, 1×RTT, WCDMA, TD-SCDMA, LTE,E-UTRAN, EVDO, HSPA, HSDPA, Wi-Fi, WiMAX, UWB, IR protocols, Bluetoothprotocols, USB protocols, and/or any other wireless protocol.

Via these communication standards and protocols, the mobile device 1300may according to various embodiments communicate with various otherentities using concepts such as Unstructured Supplementary Service data(USSD), Short Message Service (SMS), Multimedia Messaging Service(MIMS), Dual-Tone Multi-Frequency Signaling (DTMF), and/or SubscriberIdentity Module Dialer (SIM dialer). The mobile device 1300 can alsodownload changes, add-ons, and updates, for instance, to its firmware,software (e.g., including executable instructions, applications, programmodules), and operating system.

According to one embodiment, the mobile device 1300 may include alocation determining device and/or functionality. For example, themobile device 1300 may include a GPS module adapted to acquire, forexample, latitude, longitude, altitude, geocode, course, and/or speeddata. In one embodiment, the GPS module acquires data, sometimes knownas ephemeris data, by identifying the number of satellites in view andthe relative positions of those satellites.

The mobile device 1300 may also comprise a user interface (that caninclude a display 1316 coupled to a processing element 1308) and/or auser input interface (coupled to a processing element 308). The userinput interface can comprise any of a number of devices allowing themobile device 1300 to receive data, such as a keypad 1318 (hard orsoft), a touch display, voice or motion interfaces, or other inputdevice. In embodiments including a keypad 1318, the keypad can include(or cause display of) the conventional numeric (0-9) and related keys(#, *), and other keys used for operating the mobile device 1300 and mayinclude a full set of alphabetic keys or set of keys that may beactivated to provide a full set of alphanumeric keys. In addition toproviding input, the user input interface can be used, for example, toactivate or deactivate certain functions, such as screen savers and/orsleep modes.

The mobile device 1300 can also include volatile storage or memory 1322and/or non-volatile storage or memory 1324, which can be embedded and/ormay be removable. For example, the non-volatile memory may be ROM, PROM,EPROM, EEPROM, flash memory, MMCs, SD memory cards, Memory Sticks,CBRAM, PRAM, FeRAM, RRAM, SONOS, racetrack memory, and/or the like. Thevolatile memory may be RAM, DRAM, SRAM, FPM DRAM, EDO DRAM, SDRAM, DDRSDRAM, DDR2 SDRAM, DDR3 SDRAM, RDRAM, RIMM, DIMM, SIMM, VRAM, cachememory, register memory, and/or the like. The volatile and non-volatilestorage or memory can store databases, database instances, databasemapping systems, data, applications, programs, program modules, scripts,source code, object code, byte code, compiled code, interpreted code,machine code, executable instructions, and/or the like to implement thefunctions of the mobile device 1300.

The mobile device 1300 may also include one or more of a camera 1326 anda mobile application 1330. The camera 1326 may be configured accordingto various embodiments as an additional and/or alternative datacollection feature, whereby one or more items may be read, stored,and/or transmitted by the mobile device 1300 via the camera. The mobileapplication 1330 may further provide a feature via which various tasksmay be performed with the mobile device 1300. Various configurations maybe provided, as may be desirable for one or more users of the mobiledevice 1300 and the system 1020 as a whole.

The invention is not limited to the above-described embodiments and manymodifications are possible within the scope of the following claims.Such modifications may, for example, involve using a different source ofenergy beam than the exemplified electron beam such as a laser beam.Other materials than metallic powder may be used, such as thenon-limiting examples of: electrically conductive polymers and powder ofelectrically conductive ceramics.

That which is claimed:
 1. A program element configured and arranged when executed on a computer to implement a method for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article, said method comprising the steps of: providing at least one electron beam source emitting an electron beam for at least one of heating or fusing said powder material, where said electron beam source comprises a cathode, an anode, and a grid between said cathode and anode; controlling the electron beam source in a first mode when said formation of said three-dimensional article is in a first process step, wherein the first mode comprises a feed-forward mode and the first process step comprises fusing said powder material; during the fusion of said powder material, changing a predetermined grid potential from a first predetermined grid potential to a second predetermined grid potential that is different from the first predetermined grid potential; controlling said electron beam source in a second mode when said formation of said three dimensional article is in a second process step, wherein the second mode comprises a feed-back mode and the second process step comprises one of the group of: preheating the surface prior to applying a new powder layer onto said surface, preheating a new powder layer, preheating a powder distribution, or post heat treatment of an already fused powder layer; and while operating in the feed-back mode, measuring an electron beam current.
 2. The program element according to claim 1, wherein the program element is stored on a non-transitory computer readable medium.
 3. The program element according to claim 1, wherein the method implemented further comprises the steps of: applying a predetermined accelerator voltage between said cathode and said anode; applying a predetermined number of different grid potentials between said grid and said cathode for producing a corresponding predetermined number of electron beam currents; and at least one of creating or updating a look-up table or mathematical function during said second mode wherein said look-up table or mathematical function defines a relationship between a desired electron beam current and an applied grid voltage.
 4. The program element according to claim 3, wherein the method implemented further comprises the steps of: comparing a first actual electron beam current with a first desired electron beam current; and updating the at least one of the look-up table or mathematical function if the difference between said first actual and first desired electron beam currents is greater than a predetermined value.
 5. The program element according to claim 4, wherein the updating is performed after fusing a predetermined number of layers of the three-dimensional article.
 6. The program element according to claim 4, wherein the updating is performed between the fusion of each layer of the three-dimensional article.
 7. The program element according to claim 4, wherein the method implemented further comprises the step of retrieving the first predetermined potential from the at least one of the look-up table or mathematical function.
 8. The program element of claim 1, wherein said predetermined grid potential is changed from the first predetermined grid potential to the second predetermined grid potential during fusion of at least one individual scan line for changing said electron beam current in said scan line from a first value to a second desired value.
 9. The program element of claim 1, further comprising the steps of: applying a predetermined number of different grid potentials between said grid and said cathode for producing a corresponding predetermined number of electron beam currents; and at least one of creating or updating a look-up table or mathematical function during the second mode of the at least two modes based on the measured electron beam current, wherein said look-up table or mathematical function defines a relationship between a desired electron beam current and an applied grid voltage.
 10. A computer program product comprising at least one non-transitory computer-readable storage medium having computer-readable program code portions embodied therein, the computer-readable program code portions comprising at least one executable portion configured for: controlling an electron beam source in a first mode when formation of a three dimensional article is in a first process step, wherein the electron beam source emits an electron beam for at least one of heating or fusing individual layers of a powder material together so as to form said three-dimensional article, the electron beam source comprising a cathode, an anode, and a grid between said cathode and anode and wherein the first process step comprises fusing said powder material and; during the fusion of said powder material, changing a predetermined grid potential from a first predetermined grid potential to a second predetermined grid potential that is different from the first predetermined grid potential; controlling said electron beam source in a second mode when said formation of said three dimensional article is in a second process step, wherein an electron beam current from said electron beam source is controlled in a feed-forward mode in said first mode and said electron beam current is controlled in a feed-back mode in said second mode; and while operating in the feed-back mode, measuring said electron beam current.
 11. The computer program product of claim 10, wherein the at least one executable portion is further configured for: applying a predetermined accelerator voltage between said cathode and said anode; applying a predetermined number of different grid potentials between said grid and said cathode for producing a corresponding predetermined number of electron beam currents; and at least one of creating or updating a look-up table or mathematical function during said second mode wherein said look-up table or mathematical function defines a relationship between a desired electron beam current and an applied grid voltage.
 12. The computer program product of claim 11, wherein the at least one executable portion is further configured for: comparing a first actual electron beam current with a first desired electron beam current; and updating the at least one of the look-up table or mathematical function if the difference between said first actual and first desired electron beam currents is greater than a predetermined value.
 13. The computer program product of claim 12, wherein the updating is performed after fusing a predetermined number of layers of the three-dimensional article.
 14. The computer program product of claim 12, wherein the updating is performed between the fusion of each layer of the three-dimensional article.
 15. The computer program product of claim 12, wherein the at least one executable portion is further configured for retrieving the first predetermined grid potential from the at least one of the look-up table or mathematical function.
 16. The computer program product of claim 10, said predetermined grid potential is changed from the first predetermined grid potential to the second predetermined grid potential during fusion of at least one individual scan line for changing said electron beam current in said scan line from a first value to a second desired value.
 17. The computer program product of claim 10, wherein the at least one executable portion is further configured for: applying a predetermined number of different grid potentials between said grid and said cathode for producing a corresponding predetermined number of electron beam currents; and at least one of creating or updating a look-up table or mathematical function during the second mode of the at least two modes based on the measured electron beam current, wherein said look-up table or mathematical function defines a relationship between a desired electron beam current and an applied grid voltage. 